The addition of one or more previously formed resistors in series with the heater element of a thermal converter forms a micropotentiometer. The highest performance thermal converters are multijunction thermal converters (MJTCs).
Micropotentiometers are very precise standards for determining a low voltage output over a wide range of frequencies for ac-dc and RF-dc applications. To meet this need, integrated .mu.pots require physical ruggedness, ability to withstand stresses associated with thermal cycling and in-use exposure to a wide range of temperatures locally, and an error-free structure, e.g., minimization of capacitances or inductances developed between the heater and thermopiles and/or the contact pads.
The best combination for structural elements for forming MJTCs and the output resistors required for the corresponding .mu.pots includes: low stress sandwich-type multifilm membranes; low stress metal films for forming the heater element, thermopiles, contact-pads, and the like; minimization of capacitances between heater and thermopiles or between contact pads by precise definition of form and structure; a coaxial design, use of a relatively thick film nonmagnetic mounting substrate to support a chip containing thinner films constituting the heater element, thermopiles, resistors and contact pads; optional provision of guard thermocouples at both ends of each thermopile; and careful selection of materials so that, for example, the resistance heaters have a very low thermal coefficient of resistance and Thompson effect. The present invention incorporates such features in novel and highly reliable structures.
These and other related objects of this invention are described more fully hereinbelow, as are structural details of the preferred embodiments of this invention and methods of forming the same. Persons of ordinary skill in the art, upon understanding the following disclosure and the accompanying drawing figures may consider implementing obvious modifications and variations of this invention, and the claims appended hereto are intended to comprehend such variations of the explicitly disclosed embodiments.